This disclosure relates generally to diagnostic imaging and, more particularly, to an improved support structure for a computed tomography (CT) detector assembly.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan or cone-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are transmitted to the data processing system for image reconstruction. Imaging data may be obtained using x-rays that are generated at a single polychromatic energy. However, some systems may obtain multi-energy images that provide additional information for generating images.
The detector array (or assembly) and the x-ray tube are structurally mounted to the gantry. Generally, the detector is mounted in a cantilever fashion to a structural plate or integrated onto a vertical surface. That is, the rotating base of the gantry typically rotates about a patient or z-axis of the CT system, and the detector assembly is mounted axially therefrom (extending from the rotating base along the z-axis).
Such a mounting scheme has proven adequate to support the detector assembly and, although cantilever mounted, the amount of deflection has not been excessive. However, in recent years at least two changes in system design have caused an increased propensity for cantilever-mounted detector designs to deflect to unacceptable levels. First, gantry rotational speeds have increased and some image acquisitions are performed at gantry speeds of five revolutions/second or greater. Second, detector coverage in the z-direction has also increased and detectors having greater than 64 slices have been implemented. The increased length in z corresponds to a yet larger cantilever loading of the detector. As such, speed-dependent artifacts may be experienced due to this combined effect of increased cantilever loading and increased gantry speed.
In addition, as the axial length of the detector (in z) has increased, so too has the location for mounting the x-ray tube. That is, typically the x-ray tube is mounted on the gantry and on the rotating base such that its focal spot is centered axially approximately on the centermost detector in z. However, as the detectors increase in length, the x-ray tube itself is also moved axially and in accordance with the central z detector. Thus, the propensity for speed-dependent artifacts is compounded yet further, as the x-ray tube may also be supported using a longer cantilever arm, as well, which may also noticeably deflect during high speed gantry operation.
Therefore, it would be desirable to have a method and apparatus to improve mounting of components of a CT system on a gantry.